Mesoscale Precipitation Discussion 1043
NWS Weather Prediction Center College Park MD
231 PM EST Fri Dec 07 2018

Areas affected...Central Coastal Plain of TX...

Concerning...Heavy rainfall...Flash flooding possible

Valid 071930Z - 080030Z

SUMMARY...Warm sector enhanced convection with potential for
repeat tracks, may lead to isolated flooding/flash flooding
through early evening.

DISCUSSION...GOES-16 WV suite depicts leading edge of greatest
height-falls are approaching across South Texas.  This leads to
favorable eastward shift of the ridge axis and placement of the
warm sector across the coastal plain of Texas to be within the
right entrance to the 90kt 3H jet streak enhancing vertical ascent
and strengthening of low level inflow fairly orthogonal to the
frontal zone draped from N of ALI to N of VCT to deepening surface
wave NW of Houston Metro area.  Sfc inflow of 15-20kts near CRP is
advecting high Theta-E air (70F Tds) off the Western Gulf, and
CIRA LPW fields suggesting saturated profiles starting to align
over the front leading to total PWat values in the vicinity of
1.75" per GPS network.  While cloud cover has limited solar
insolation, temps to 75F support 750-1250 J/kg of SBCAPEs with
consistent replenishing flow, though slowly veering with time. 

10.3 um channel has shown continual shield of cooling tops, but
now embedded overshooting CBs in Bee/Goliad county have reached
-65C increasing the vertical depth for rainfall generation, likely
indicating rates up to 1.75"/hr are probable in the next few
hours.  Cell motions to the NE at 20kts are likely to limit the
duration at any given point to produce flash flooding, but it is
the veering wind profiles and persistent and slowly increasing LLJ
as the main height-falls approach that should support additional
upstream development.  As such repeat tracks are possible
especially near coastal zones where enhanced convergence from
friction at bay/inlet/cove intersections are likely to aid in the
redevelopment process.

Limiting factor is clearly dry antecedent conditions across the
region, though reduced soil infiltration due to transition to
winter ground conditions may support more runoff than FFG values
would suggest, still flash flooding should be limited in scale and
coverage, even the most aggressive Hi-Res CAMs such as the
GEM-Regional, HRRR and HRRR-Experimental are only 2-3" through
00z, from San Patricio to Wharton/Matagorda county.  Observational
trends are favoring these models' orientation and evolution to
suggest flash flooding may be possible through evening hours.

Gallina

ATTN...WFO...CRP...EWX...HGX...

ATTN...RFC...WGRFC...

LAT...LON   29819615 29669553 29529527 29249510 28999519
            28809539 28439620 28059679 27569715 27359741
            27429774 27619799 28339798 28779780 29149756
            29459719 29739667